This invention generally relates to electric motor control. More particularly, this invention relates to determining the position and rate of selected motor system components and compensating for errors associated with using such determinations in motor control signals especially in the case of high motor speed.
Electric motors are well known and in widespread use. Depending on the needs of a particular application, one of several motor types may be utilized. Each motor type has advantages or benefits for certain applications. Regardless of the motor type chosen, appropriate motor control is required to achieve the intended results.
One important aspect of motor control is providing control signals with proper timing and polarity to achieve the desired motor rotation direction and speed. Typical arrangements include a position indicator such as a resolver that provides “feedback” information to the motor controller for adjusting the control signals as may be needed.
One significant drawback to conventional arrangements is that they rely upon complex computations utilizing the position indicator information. In one example, a microprocessor is programmed to calculate a position based upon a complex relationship between two analog outputs from a resolver. This not only introduces complexity into the system but also requires relatively more expensive electronics. In most situations, simplicity and cost savings are very desirable.
Moreover, conventional techniques typically are not capable of providing the level of accuracy needed for some motor control applications. Various error sources introduce inaccuracies in position and velocity determinations. One source of error is latency associated with the delays between data gathering and signal processing because the motor parts are constantly moving. Latency typically cannot be avoided. Motors that rotate at higher speeds, for example, require even faster signal processing to keep up with the faster changing positions of the motor components in a manner that would avoid the effects of latency.
Other sources of error include a conversion time error that is a function of the time it takes to convert position information into useable form. The conversion time error is most significant when the component of interest transitions between the end of one revolution and the beginning of a subsequent revolution. Other errors are associated with the typically required analog and digital signal processing in motor control systems.
This invention provides a unique solution to the problem of achieving accurate motor control using efficient and reliable position determination and correcting for errors otherwise associated with signal processing. This invention provides the ability to accurately determine position information, velocity information, or both and to compensate for positional computation errors, velocity computation errors or both. The inventive approach provides substantial cost savings as the computational requirements are reduced, which permits the use of less expensive electronics.